There are many situations in which it is advantageous to monitor sounds emitted at a remote location. For example, certain machinery, such as compressors or electrical generators, makes characteristic sounds when operating properly. A change in this characteristic sound is often an early indication of malfunction. This machinery can't always be monitored locally, at least not on a consistent basis. Reproducing the sound at a remote location where the presence of personnel is more constant allows for better supervision of the machinery.
Likewise, the supervision of a sleeping infant can also be performed more reliably when the infant's sounds are monitored remotely. While the infant is sleeping, a parent or babysitter can relax in another room while still monitoring sounds that the infant makes. If the infant wakes up momentarily, the parent is notified and can make sure that the infant gets back to sleep. When the infant is ready to end his nap, or is finished resting quietly and wants to be fed, the parent can hear the infant crying and get him out of his crib.
One advantage to having a remote reproduction of the infant's sounds is that the person supervising the infant can hold a conversation at a normal level, or watch television, without worrying that the sound level will cause the infant to wake up. However, this means that the monitor sound level must be turned up to be heard over any other sound, which can be distracting, particularly because at high sound levels, many conventional monitor receivers have poor sound quality. Further, if a babysitter is engaged in a telephone conversation or other activity that requires her to listen and commands her attention, supervision of the infant could be compromised.
It would therefore be beneficial to provide a remote sound monitor that provides an indication of the sound being monitored, but doesn't always require the supervisor's hearing or direct attention. For example, a visual indication that gives an immediate indication of a change in sound level being monitored and that can be observed from various vantage points in the vicinity of the receiver would be advantageous.